Systems and assemblies for forming a deformable material, such as a sheet of metal, into a desired profile are known. One such system, known as roll forming, is a well established process used in many industries, such as automotive and construction industries, to produce simple and complex shapes from a sheet of metal. Examples of some profiles 10, 11 and 12 produced by roll forming are provided in FIG. 1.
With reference to FIGS. 2A through 2C, roll forming includes passing a continuous sheet 20 through a series of spaced roll sets 21a through 21f. Each roll set 21 progressively deforms the sheet 20 to the desired final profile 22. Each roll set 21 includes at least one upper roll 23a through 23f, and at least one lower roll 24a through 24f. In some instances, side rolls 25 may also be provided, depending on the desired final profile 22.
As mentioned above, the rolls 23, 24 and 25 are designed such that the sheet of material 20 is progressively deformed to the final profile 22. In order to achieve this deformation, the roll sets 21 must be spaced at predetermined distances to facilitate sufficient deformation and relaxation between the roll sets 21. This disadvantageously results in wasted deformation energy. Also, the roll forming process inherently involves strain path differences due to unnecessary axial bending and stretching between each roll set 21. Axial plastic bending and stretching lead to product defects as shown in FIGS. 3A through 3D. These defects include so-called edge wave (FIG. 3A), flare (FIG. 3B), sweep or camber (FIG. 3C) and twist (FIG. 3D). Roll forming also has disadvantages in that the surface of the sheet of material being formed is placed under stresses due to stretching of the material. In the case of a coated metal, for example, this may have deleterious effects on the quality of the surface finish.
Roll forming has another disadvantage in that the distance between the first roll set 21a and the last roll set, in this case 21f, is relatively large. As a result, the space needed to house a roll forming assembly is substantial, particularly when forming of complex profiles is required. Moreover, a specific set up of roll sets 21 is required for each desired final profile 22. Consequently, it is not a simple process to set up a roll forming assembly, nor is it possible to simply exchange roll sets 21 to produce a different final profile 22.
Alternatives to traditional roll forming assemblies, as described above, have been proposed, for example in German Offenlegungsschrift No. 2 423 279 and European Patent No. 0 384 287.
German Offenlegungsschrift No. 2 423 279 describes a press forming assembly that includes an upper die and a lower die. Each of the upper and lower dies has a profile extending longitudinally along the length of the dies, the profiles of the upper and lower dies being complementary and designed to produce a desired final profile. More particularly, the profiles of the upper and lower dies are such that a sheet of deformable material, generally metal, fed to the assembly is progressively deformed along the longitudinal length of the sheet of material.
Deformation of the sheet of material is achieved by pressing the upper and lower dies together, for example using an eccentric cam (illustrated in FIG. 19 of this document), or using pivoting arms attached to the sides of the upper and lower dies (illustrated in FIG. 28 of this document).
Likewise, European Patent No. 0 384 287 describes an assembly that includes upper and lower dies that are designed to progressively deform a sheet of material by pressing the dies together using an eccentric cam.
In both instances, the upper and lower dies engage and disengage the sheet material to be deformed along a processing length. As the sheet is engaged, having been displaced horizontally through the upper and lower die set during the disengagement operation, the sheet is progressively deformed to the final profile.
The present invention aims to provide an alternative press forming assembly and method to those described above. The assembly and method of the invention advantageously avoid or alleviate problems associated with unnecessary deformation of the deformable material that may be observed during disengagement of the material during processing. The invention also aims to provide a method of fabricating a die set suitable for use in such an assembly and method.